It is a long-standing objective of color photographic origination materials to maximize the overall response to light while maintaining the lowest possible granularity. Increased photographic sensitivity to light, commonly referred to as photographic speed, allows for improved images captured under low light conditions or improved details in the shadowed regions of the image. In general, the overall light sensitivity provided by the light sensitive silver halide emulsions in such systems is determined by the size of the emulsion grains. Larger emulsion grains capture more light. Upon development, the captured light is ultimately converted into dye deposits that constitute the reproduced image. However, the granularity exhibited by these dye deposits is directly proportional to the sizes of the silver halide grains. Thus, larger silver halide grains have higher sensitivity to light but also lead to higher granularity in the reproduced image. Therefore, it is a fundamental problem in photography to improve the light sensitivity of a silver halide element without changing the silver halide emulsion.
One partial solution to the problem is to coat an addendum in the film as described in U.S. Pat. No. 6,319,660. The described addenda that contain at least three heteroatoms provide speed increases, but they also degrade interimage effects thereby reducing color saturation and reproduction. Furthermore, when the addenda are incorporated directly in melts with the light sensitive halide emulsion, large speed losses instead of speed gains are seen. These are the specific problems to solve. What is needed is a photographic element that will deliver a higher speed with a given emulsion, without concomitant loss of interimage, or without the need to incorporate addenda by placing them in coating melts that are separate from the light sensitive silver halide emulsion.
U.S. Pat. No. 6,319,660 describes speed-improving compounds with at least three heteroatoms in a layer that contains a light-sensitive silver halide emulsion, or in a nonsilver-containing light insensitive layer. Among the speed improving compounds described are diazoles, and the most preferred diazoles include the 1-thia-3,4-diazoles where the C-5 substituent is a mercapto (—SH) group and the C-2 substituent is an alkyl, aryl, alkylthio, arylthio, or amino group. Compound BJ in U.S. Pat. No. 6,319,660 is such an exemplified mercaptothiadiazole that in Example 3 showed increased photographic sensitivity. However, these types of speed improving compounds suffer from two deficiencies.
The first problem is that the compounds of U.S. Pat. No. 6,319,660 give speed enhancements only when they are not mixed directly with the light sensitive silver halide emulsion prior to coating. When the compounds are mixed with the silver halide emulsion and the combination is held for a significant period of time before coating (commonly referred to as a single melt coating), the compounds in U.S. Pat. No. 6,319,660 give a speed loss, not a gain. For successful use, the compounds in U.S. Pat. No. 6,319,660 must be kept separate from the silver halide emulsion prior to coating and only mixed together immediately prior to the coating operation. This requires the preparation of two separate solutions that is undesirable. This undesirable coating procedure is called a dual-melt coating.
A second problem with the use of the compounds in U.S. Pat. No. 6,319,660 is that desirable interlayer interimage effects (IIEs) are diminished. For example, it is often desirable for color rendition that exposure to red or blue light will reduce green density being formed in green light sensitive sublayers. When the compounds in U.S. Pat. No. 6,319,660 are used in the green sublayers to increase the speed of those layers, the amount of green density suppression as a function of blue or red light exposure is less, and this is undesirable.
U.S. Pat. No. 5,187,054 describes ballasted heterocyclic compounds useful as antisludging agents. Typically, the compounds are azole derivatives that contain a ballast group to prevent diffusion of the compound. However, the compounds must be contained in a nonlight-sensitive layer, preferably the topmost nonlight-sensitive layer.
U.S. Pat. No. 6,190,848 describes art in which triazoles with Log Kow (see description of Log Kow below) from 4.75 to 9.0 are used in a light sensitive emulsion layer in combination with a second light sensitive layer that contains a compound that imagewise releases inhibitors with certain properties to improve interimage effects. However, the triazoles described within have insufficient Log Kow to cause speed increases and as noted (Column 7, lines 12-18), their laydown must be minimized in order to prevent excessive speed losses.
U.S. Pat. No. 6,140,029 describes a nonlight sensitive layer that contains elemental silver and a ring system that contains at least three nitrogen atoms, at least one N—H bond, and a Log Kow at least 4.5.
U.S. Pat. No. 6,228,572 describes a light sensitive layer that contains either a mercapto-oxadiazole, mercaptothiadiazole or mercaptoselenodiazole or their salts in combination with a second light sensitive layer that contains a compound that imagewise releases inhibitors with certain properties to improve interimage effects. It is a problem to be solved to provide a silver halide photographic element that contains an addenda that affords improved speed with little or no reduction in interimage effects and with improved melt-hold stability.